Ask David and Farrar: Technical Questions and Advice About Carbureting a DeLorean

[NightFlyer]

Isn't he running a different block?

I believe he is, thus for I all I know, his compression could also be different, which would substantially effect power, though he never mentions this as being a reason as to why his car is faster....

[Andrew]

He is running a different engine. I was researching the carb topic and found a post in which he detailed the different engine mounts. From what I read the engine started its life as a carburated Peugeot barge powertrain. I don't know whether the compression is the same however.

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[NightFlyer]

He is running a different engine. I was researching the carb topic and found a post in which he detailed the different engine mounts. From what I read the engine started its life as a carburated Peugeot barge powertrain. I don't know whether the compression is the same however.

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OK - yeah, I should have known that, as he constantly references how his engine doesn't have any injector bungs.

[DCUK Martin]

You can't run a stock exhaust with a carb or you'll kill the catalyst. A less restricted intake is about all you gain with a carb all other things being equal

[NightFlyer]

You can't run a stock exhaust with a carb or you'll kill the catalyst. A less restricted intake is about all you gain with a carb all other things being equal

OK, I'll bite.

Why can't you run a DeLorean catalytic converter in conjunction with a carb? Is there something special about the D's cat vs the millions of other carbureted cars that use a catalytic converter in their exhaust systems? I don't get why the cat would care one way the other about the method of fuel delivery that the engine is utilizing.

In my mind anyway, the cat would only care about how complete of a combustion you're achieving of the air/fuel mixture during the power stroke, which is a function of compression and ignition, but nothing at all to do with the method of fuel delivery to the intake.

So, what am I missing here?

[DCUK Martin]

The delorean has a 3 way cat. Accurate mixture control in both directions is essential to maintain emissions and the catalyst. Some late carb systems have some form of closed loop system as I understand it but they're rare

[Farrar]

If you want more power from your engine, you will need to change the engine itself, not its method of fuel delivery. The only difference I noticed when I went from K-Jet to carb on my stock engine was a slightly faster throttle response. The reason I went to carb in the first place was so that I would have a running DeLorean while I could fix other stuff -- I was having some difficulty keeping up with all the stuff on the car that needed attention at the same time that K-Jet was beginning to break down. That's just my experience.

There are more performance upgrades for the PRV available now than ever before, including freer-flowing header/exhaust, turbochargers, and cams. I think DPI has even installed a 3.0L with supercharger at one point. Those upgrades cost more money than a carburetor, but will get you REAL performance.

As for catalytic converters, I still have the catalytic converters on my car that were installed in 2004. I have been carbureted since 2008. However, I have probably put less than 10,000 miles on the car since the change to carburetor, and I tend to jet my carb for economy rather than performance. (Not much point in expecting performance from my car -- it's an automatic.)

I wouldn't take the decision lightly. A carburetor is not a magic bullet. It is only part of one system on the car. If you are having problems with K-Jet and you are a "carb guy" and find carburetors easier to understand and work on, then you might wish to switch. However, if you're having other problems that are not related to fuel-delivery, my advice is to fix those first, and then see if you're not really that fed up with K-Jet after all.

Bottom line: If you are experiencing a lack of power, I would rule out fuel delivery as a source of that problem before considering making any changes.

[NightFlyer]

The delorean has a 3 way cat. Accurate mixture control in both directions is essential to maintain emissions and the catalyst. Some late carb systems have some form of closed loop system as I understand it but they're rare

So then all the owners who are running their lambda systems open loop with k-jet are in essence killing their catalytic converters, right?

And yet, I've never heard of any of those owner's failing an emissions test or having a back-pressure issue due to a plugged up catalyst.

Not to mention that several owners who have converted over to carbs are still running their stock exhaust, and to my knowledge anyway, not a single one has reported any catalyst related problems/issues.

The theory appears to be that precise mixture control is necessary for the catalyst to survive, however, the practical experience of such is that perhaps the catalyst is a bit more robust than the theory suggests - would that be a fair assessment?

[NightFlyer]

If you want more power from your engine, you will need to change the engine itself, not its method of fuel delivery. The only difference I noticed when I went from K-Jet to carb on my stock engine was a slightly faster throttle response. The reason I went to carb in the first place was so that I would have a running DeLorean while I could fix other stuff -- I was having some difficulty keeping up with all the stuff on the car that needed attention at the same time that K-Jet was beginning to break down. That's just my experience.

There are more performance upgrades for the PRV available now than ever before, including freer-flowing header/exhaust, turbochargers, and cams. I think DPI has even installed a 3.0L with supercharger at one point. Those upgrades cost more money than a carburetor, but will get you REAL performance.

As for catalytic converters, I still have the catalytic converters on my car that were installed in 2004. I have been carbureted since 2008. However, I have probably put less than 10,000 miles on the car since the change to carburetor, and I tend to jet my carb for economy rather than performance. (Not much point in expecting performance from my car -- it's an automatic.)

I wouldn't take the decision lightly. A carburetor is not a magic bullet. It is only part of one system on the car. If you are having problems with K-Jet and you are a "carb guy" and find carburetors easier to understand and work on, then you might wish to switch. However, if you're having other problems that are not related to fuel-delivery, my advice is to fix those first, and then see if you're not really that fed up with K-Jet after all.

Bottom line: If you are experiencing a lack of power, I would rule out fuel delivery as a source of that problem before considering making any changes.

That's good advice

[Nicholas R]

So then all the owners who are running their lambda systems open loop with k-jet are in essence killing their catalytic converters, right?

And yet, I've never heard of any of those owner's failing an emissions test or having a back-pressure issue due to a plugged up catalyst.

Not to mention that several owners who have converted over to carbs are still running their stock exhaust, and to my knowledge anyway, not a single one has reported any catalyst related problems/issues.

The theory appears to be that precise mixture control is necessary for the catalyst to survive, however, the practical experience of such is that perhaps the catalyst is a bit more robust than the theory suggests - would that be a fair assessment?

Well... actually, in 2007, my car was running open loop on thanksgiving, and I was driving home when the car stalled. I got out to look at the engine and could see something glowing under the car. It was my catalytic converter glowing red. I remember this vividly because neither my mother or my girlfriend at the time were happy about the possibility of us missing thanksgiving dinner due to, (as it was commonly referred to at the time), "that f&*$in' DeLorean. (it wasn't that reliable back then)

Turned out I was running lean due to plugged injectors, melted the catalyst, and all but completely plugged up the cat. I was able to limp the car home, driving a few minutes, then stopping to let it cool. Later on I pulled the exhaust off the car and completely hollowed out the plugged catalytic converter. I still always ran open loop after that, but always made a point to set the mixture by using the voltage from the O2 sensor, instead of just what sounded good.

I know this is just one instance but it's still one